1. Field of Invention
This invention is directed to solid surface materials having antibacterial properties.
2. Description of the Related Art
Artificial (or synthetic) marble can be considered as a general designation for various types of materials used as building products, such as bathroom vanity tops, sinks, shower stalls and kitchen counter tops, for example; furniture; sanitary use; lining materials; and stationary small articles. Also, from a viewpoint that the artificial marble is clean and neat, it has recently been used in hospitals, nursing homes, as well as commercial and residential food preparation facilities etc. Artificial marbles encompass cultured marble, onyx and solid surface materials typically comprising some kind of resin matrix and either with or without a filler present in the resin matrix. Typically, cultured marble consists of a gel coating of unfilled unsaturated polyester on a substrate of a filled unsaturated polyester, the filler generally being calcium carbonate, or the like. Onyx typically consists of a similar unfilled gel coat on a substrate of filled unsaturated polyester, the filler being alumina trihydrate (ATH). Solid surface materials are typically filled resin materials and, unlike cultured marble or onyx, do not have a gel coat. Corian(copyright) material available from E. I. du Pont de Nemours and Company, Wilmington, Del. (DuPont) is a solid surface material comprising an acrylic matrix filled with ATH.
As evidenced by the presence in the market of numerous materials for eliminating or minimizing human contact with bacteria, there is clearly a demand for materials and/or processes that either minimize or kill bacteria encountered in the environment. Such materials are useful in areas of food preparation or handling and in areas of personal hygiene, such as bathrooms. Similarly, there is a use for such antibacterial materials in hospitals and nursing homes where people with lowered resistance are especially vulnerable to bacteria.
Cultured marbles have been developed wherein an antibacterial agent has been incorporated in the gel coat, but not through the matrix of the substrate. Such materials have been disclosed in Japanese Patent Application Publication Kokai: 7-266522. However, such materials have a relatively thin gel coat, typically in the order of 15 mils and, as such, when the gel coat is depleted of antibacterial agent or the gel coat wears away or is otherwise removed, the antibacterial effect is significantly decreased or lost entirely.
With regard to solid surface materials consisting of either an unsaturated polyester resin or an epoxy resin there has not been any use of an antibacterial agent included throughout the resin.
This invention is directed to a solid surface material with an outer surface having a restorable antibacterial effectiveness. This solid surface material includes a matrix of at least one resin, at least one filler dispersed in the matrix, and at least one antibacterial agent dispersed in the matrix. The resin can be thermoset, thermoplastic, or combinations thereof. The antibacterial agent is present in an amount that provides an outer surface of the solid surface material with an antibacterial effectiveness within about 24 hours. The antibacterial agent can be an inorganic compound, an organic compound, or a combination thereof. It has been found that the outer surface has an antibacterial effectiveness which can diminish and that the antibacterial effectiveness can be restored by removing a portion the outer surface, preferably by abrading the outer surface.
The present invention also relates to a method for restoring the antibacterial effectiveness of a solid surface material of the present invention, wherein the solid surface material has an outer surface, at an initial time (t0), with an initial antibacterial activity value within 24 hours of sample incubation (xcex94t0@24 h) that is greater than zero, wherein at a first later time (t1), wherein t1 greater than t0, the outer surface has a first later antibacterial activity value within 24 hours of sample incubation (xcex94t1@24 h) wherein (xcex94t1@24 h) is less than (xcex94t0@24 h), the method comprising: at a second later time (t2), wherein t2 greater than t1, actively removing a portion of the outer surface of the solid surface material to provide a second outer surface on the solid surface material, the second outer surface having a second later antibacterial activity value within 24 hours of sample incubation (xcex94t2@24 h) such that it satisfies the Equation I below:
(xcex94t2@24 h) greater than 0 and (xcex94t2@24 h) greater than (xcex94t1@24 h)xe2x80x83xe2x80x83Equation (I);
wherein the active removal step can be repeated whenever necessary to continuously restore the antibacterial effectiveness of the solid surface material.
In a preferred embodiment, the restoration method includes at least one active removal step, which can be achieve by abrading or ablating away the surface.
The artificial marbles of the present invention are made from a curable composition containing at least one antibacterial agent. The artificial marble materials of this invention are effective in inhibiting or destroying many common bacteria encountered in the home, and health care or food preparation environments. The term xe2x80x9cantibacterialxe2x80x9d is understood to be interchangeable with the term xe2x80x9cantimicrobialxe2x80x9d and other such like terms as would be familiar to one of ordinary skill. The term xe2x80x9cantibacterial effectivenessxe2x80x9d is intended to mean that, given a sufficient amount of antibacterial agent, the microbial concentration of a sample is decreased by at least about 30% over a period of time. It is known that the actual antibacterial effectiveness of an antibacterial agent depends upon the specific resin matrix used and the specific bacteria tested. The term xe2x80x9cartificial marblexe2x80x9d has been defined in the previous section. The term xe2x80x9csolid surface materialsxe2x80x9d include those useful for decorative solid surfaces such as, for example, those used as building products, such as bathroom vanity tops, sinks, shower stalls and kitchen counter tops; furniture; sanitary use; lining materials; and articles such as office supplies.
The types of resin matrices useful in the present invention include both thermoplastic resins, thermoset resins and combinations thereof. Examples of thermoplastic resins include olefins, such as low and high density polyethylene and polypropylene; dienes, such as polybutadiene and Neoprene(copyright) elastomer; vinyl polymers, such as polystyrene, acrylics, and polyvinyl chloride; fluoropolymers, such as polytetrafluoroethylene; and heterochain polymers, such as polyamides, polyesters, polyurethanes, polyethers, polyacetals and polycarbonates. Examples of thermoset resins include phenolic resins, amino resins, unsaturated polyester resins, epoxy resins, polyurethanes and silicone polymers.
Epoxy resins useful in the present invention include those based on epoxide groups having certain reactivity. Such materials may include epoxy resins of bisphenol type A, bisphenol type F, phenol novolak type, alicyclic epoxy, halogenated epoxy, and cycloaliphatic epoxy resins.
Unsaturated polyester resins useful in the present invention include those wherein the reactivity is based on the presence of double or triple bonds in the carbon atoms. Unsaturated polyester resins are formed by the reaction of molar amounts of unsaturated and saturated dibasic acids or anhydrides with glycols. The unsaturation sites can then be used to cross-link the polyester chains, via vinyl containing monomers such as styrene, into a thermoset plastic state.
As is known to those of ordinary skill in the art, there can be many additives to epoxy or unsaturated polyesters. Typically, such materials are cured by adding cross-linking agents and catalysts to enhance the crosslinking action.
Acrylic resins useful in the present invention are not specially limited as long as it can be formed into an acrylic solid surface material by curing. Examples of useful acrylic resins include various kinds of conventional acrylic group monomers, acrylic group partial polymers, vinyl monomers for copolymerization other than acrylic group monomers, or partial polymers. As the acrylic group monomer, (meth)acrylic ester is preferable. Also, in this specification, xe2x80x9c(meth)acrylicxe2x80x9d means xe2x80x9cacrylic and/or methacrylicxe2x80x9d.
Examples of (meth)acrylic esters include methyl (meth)acrylic ester, ethyl (meth)acrylic ester, butyl (meth)acrylic ester, 2-ethylhexyl (meth)acrylic ester, benzyl (meth)acrylic ester, glycidyl (meth)acrylic ester.
An example of a useful solid surface materials including acrylic resin is the Corian(copyright) material, which includes a poly(methyl methacrylate) (PMMA) resin with ATH as a filler. Corian(copyright) material can contain pigments, reground Corian(copyright) material in particulate form and other additives as can be found in U.S. Pat. Nos. 3,847,865 and 4,085,246, both of which are incorporated by reference.
In accordance with the present invention, at least one antibacterial agent is dispersed in the matrix in an amount that provides the solid surface material with an outer surface that has an antibacterial effectiveness. The antibacterial agent is provided in an amount that results in an outer surface having an antibacterial effectiveness within about 24 hours. The amount of antibacterial agent is preferably at least about 0.1% by weight of the precured total composition and more preferably at least about 0.5% by weight of the precured total composition. Antibacterial agents can be inorganic or organic. Types of inorganic antibacterial agents that are useful in the present invention include, but are not limited to metals and metal oxides, preferably silver, copper and zinc; metal phosphates; and metal zeolites. Specific examples of inorganic antibacterial agents include zinc oxide powder, a mixture of zinc oxide (about 70%) and partially silver and sodium ion-exchanged zirconium phosphate (about 30%), such as those available under the tradename Novaron AGZ330 (hereafter Novaron), available from Toagosei Co., Ltd., Tokyo, Japan; a mixture of zeolite and silver oxide/zinc oxide, such as those available under the tradename Zeomic, available from Shinanen Zeomic Co. Ltd., Nagoya, Japan; a mixture of calcium phosphate and zinc oxide, silver-copper zeolites, silver-zinc zeolites or silver zeolites, such as those available under the tradename Bactekiller AC, Bactekiller AZ and Bactekiller A, respectively, by Kaneko Ltd., Osaka, Japan and compounds as described in U.S. Pat. No. 5,180,085, which are inorganic core particles having a first coating of a metal or metal compound with a second coating of silica, silicate, borosilicate, alumino-silicate, alumina, aluminum phosphate, or mixtures thereof, wherein the inorganic core particles can be any of the oxides of titanium, aluminia, zinc or copper; or sulfates of calcium, strontium or barium; zinc sulfide; copper sulfide; zeolite; mica; talc; kaolin; mullite; or silica and wherein the metal or metal compounds of the first coating comprise silver, silver oxide, silver halide, copper, copper (I) oxide, copper (II) oxide, copper sulfide, zinc oxide, zinc sulfide, zinc silicate, and mixtures thereof. The metal or metal compounds and also the second coating can be present in amounts of 0.05 to 20% by weight based on the core particles. Examples of such antibacterial agents are Microfree(copyright) brand AMP-T588 (T588) which is silver, copper oxide and zinc silicate coated on titanium dioxide and overcoated with silica and aluminum hydroxide; and Microfree(copyright) brand AMP-Z200 (Z200) which is silver coated on zinc oxide and overcoated with silica and aluminum hydroxide, all of which were developed by DuPont; and Apacider AW, which is a zinc phosphate and calcium phosphate with admixture of silver and silica, available from Sangi Company Ltd., Tokyo, Japan. Types of organic antibacterial agents that are useful in the present invention include, but are not limited to halogenated compounds, phenols, quaternary ammonium salts, organotin compounds, phosphoric acids and phosphoric acid esters. Specific examples of organic antibacterial agents include the bis(2-ethylhexyl)ester of phosphoric acid with 2,2xe2x80x2-(cocoalkylimino)bis(ethanol) available under the tradename Intersept(copyright) from Interface, Kennesaw, GA or 3,5,3xe2x80x2,4xe2x80x2-tetrachloro-salicylanilide, available under the tradename Irgasan(copyright) from Ciba (formerly Ciba Geigy) of Greensboro, N.C., 5-chloro-2-(2,4-dichloro-phenoxy)phenol, available under the trademark Microban(copyright) from Microban Products Company of Huntersville, N.C. It is understood that the present invention encompasses the use of inorganic and organic antibacterial agents either alone or in any combination.
In case zinc oxide powder is used alone, its average particle diameter is preferably about 0.2-100 xcexcm, more preferably about 0.2-50 xcexcm, and especially preferably about 0.2-10 xcexcm. The amount of antibacterial agent to be used is more preferably about 0.1-10.0 percent by weight based on the weight of the precured total composition. Furthermore, the lower limit of the amount to be used is preferably at least about 0.3 percent by weight, more preferably at least about 0.5 percent by weight, based on the weight of the precured total composition. The upper limit is preferably at most about 8.0 parts by weight, based on the weight of the precured total composition.
Fillers useful in the present invention include, for example, ATH, alumina monohydrate(AMH), Bayer hydrate(BayH), silica (SiO2), magnesium hydroxide (Mg(OH)2), calcium carbonate (CaCO3), barium sulfate (BaSO4) or decorative agents, as a list that is not exhaustive and not intended to limit the invention. Fillers can be present in effective amounts from as low as about 20% up to about 75% by weight. Typically, but not necessarily, the amount of filler is decreased by the weight percent of antibacterial agent added.
It has been found that solid surface material containing PMMA with ATH as a filler exhibited a synergistic effect when certain zinc oxide-containing antibacterial agents were added to the acrylic matrix. In particular, acrylic artificial marble including zinc-oxide containing antibacterial agents have been found to have antibacterial characteristics against methicillin-resistant staphylococcus aureus (MRSA). In addition using certain other fillers and/or certain other antibacterial agents in resin matrix of the present invention other than PMMA also achieved an antibacterial effectiveness in solid surface materials.
It is known to include in solid surface materials other additives such as pigments, dyes, flame retardant agents, parting agents, fluidizing agents, viscosity control agents, curing agents, antioxidants, and the like as may be known to those of ordinary skill in the art.
Solid surface materials of this invention are typically produced by casting into a sheet form or casting into a shape form such as a sink, for example. Solid surface materials of this invention can also be produced by, for example, compression molding, injection molding or extrusion.
The problem of loss of antibacterial effectiveness in solid surface materials had not been previously addressed. It was found that the solid surface materials of this invention can lose some or all antibacterial effectiveness with time and use when an outer surface is exposed to, for example, common household or commercial cleaning agents, other liquids or heat. An outer surface is considered here to be the surface that is exposed to the environment and that is subject to use, for example, the exposed surface of a countertop. It has been discovered in accordance with this invention that the antibacterial effectiveness which is diminished with time and use can be restored by removing a portion of the outer surface of the sheet or shape.
xe2x80x9cRemoving a portion of the outer surfacexe2x80x9d can be achieved by any active removal methods, including, for example, abrading or ablating away the surface. In addition, xe2x80x9cremoving a portion of the outer surfacexe2x80x9d further includes breaking the solid surface material apart and thereby exposing a new, previously unexposed, surface.
Abrading is the physical removal of the surface, and can be achieved with actions such sanding (as with an abrasive), grinding (as with a material having a higher hardness value than the surface), planing (which includes chipping and scalping, as with a planer tool), routing (as with a router tool), blasting (as with a blasting material), and combinations thereof. The accepted definitions of these previous terms, exemplifying abrading, can be found in the Webster""s Third New Internaiontal Dictionary (Merriam-Webster Inc. 1986). Examples of useful abrasive or grinding material include sand paper and a sponge-form grinder (e.g., Scotch-Brite(copyright) Sponge, available from 3M of St. Paul, Minn.). Removal by planing is often used to remove portions of a planar surface, whereas removal by routing is often used to remove portions of an edge surface. Removal by blasting can be accomplished using any blasting material that can be xe2x80x9cblastedxe2x80x9d against a surface and thereby remove the top layer. Examples of blasting materials include, but are not limited to, sand, ground walnut shells, any ground polymer such as ground polymethylmethacrylate and ground filled polymers, and ground glass.
Removal by ablation includes chemical removal or removal by energy impingement. Chemical removal of the surface can be achieved with actions such as chemical etching. Chemical etching involves the use of a chemical compound capable of chemically reacting with the solid surface material. For example, suitable etchants for Corian(copyright) solid surface include, but are not limited to, methyl ethyl ketone (MEK), acetone, N-methylpyrrolidone. Removal by energy impingement can be achieved using a laser. When a laser energy source is used, the laser beam generated is applied to the portion of the outer surface that is intended to be removed. The frequency and intensity of the energy supplied to the material affects the amount of surface removal.
Preferably, restoration of the antibacterial effectiveness (xe2x80x9crestorationxe2x80x9d) is achieved by abrading the outer surface with an abrading material including components having a hardness greater than the cured product. Preferably, the restoration removes between about 1 and about 28 microns, more preferably between about 2.5 and about 25 microns, even more preferably between about 10 and about 25 microns of thickness from the outer surface. A useful tool of determining the amount of abrading required is to place a mark on the surface with a permanent marker, and abrading until the mark is completely removed. Of course, it is understood that only abradable surfaces can be restored in accordance to the present invention.